The present invention relates generally to fabrics, and more particularly to electric heating fabrics such as warming blankets.
In general, a warming blanket, also called an xe2x80x9celectric blanket,xe2x80x9d or an xe2x80x9celectric heating blanket,xe2x80x9d is a blanket or another fabric material having an insulated electric heating element. The heating element is typically provided as one or more metallic wires threaded in a serpentine pattern throughout the blanket or arranged as a collection of parallel wires. The shape and size of the metallic wires varies, and in some cases the wires can actually be small metallic threads.
A warming blanket is typically plugged into a power outlet so that power may be supplied to the heating element, causing the production of heat. In this manner, the warming blanket may be a warm, comfortable cover used to warm a bed or may be wrapped around an individual as a heated, comfortable throw blanket, for example. A separate category of electrically heated bedding includes mattress pads. Mattress pads are typically placed under the warming blanket are utilized to warm the bed before use or to provide comfortable heat in the event the user does not wish to be covered with a fabric.
Contemporary warming blankets usually include a user control, such as a dial, that permits a user to set the amount of heat output of the blanket. This feature allows the consumer to set the blanket to a setting that offers the desired amount of heat for a particular temperature and in accordance with the comfort level of the individual.
The present invention provides a warming blanket having a temperature sensing wire threaded through the warming blanket to sense the temperature of the warming blanket. The warming blanket may alternatively be any type of warming fabric, such as a heated throw, mattress pad, heating pad, car seat heater, as examples. In accordance with one aspect of the present invention, the temperature sensor is a positive temperature coefficient (PTC) device that is threaded throughout the blanket fabric.
In accordance with one embodiment of the present invention, the temperature sensing wire runs transverse to the heating wires in the warming blanket. This feature permits the temperature sensing wire to measure an average blanket temperature, because the temperature sensing elements cross portions of the blanket that have heating wires, and portions that do not have heating wires.
In accordance with another embodiment of the present invention, the heating element is supplied as a pair of buss wires extending along opposite sides of the warming blanket and having a number of heating wires extending therebetween. In this embodiment, the temperature sensing elements may run either parallel to or transverse to the heating elements.
Information from temperature changes in the temperature sensing element of the present invention may be provided to a microcomputer so that the microcomputer may adjust the heat output of the heating element in the warming blanket. In this manner, the temperature sensing wire and the microcomputer behave similar to a thermostat. If PTC is used as the heat-sensing material for the temperature sensing element, in one example a reference voltage (e.g., 5 volts) is applied to a length of the PTC element. Because resistance of the PTC material changes with changes in temperature, the current flowing through the PTC sensing element will increase or decrease as a result of temperature changes. The current change may be measured, and correlates with temperature changes in the PTC element, either locally or over long lengths of the sensing element.
In one embodiment of the invention, the end of the PTC sensing element opposite the end where voltage is applied is connected to a fixed resistor, which in turn is connected to ground. A voltage signal is tapped from a point between the PTC sensing element and the fixed resistor, and information about the voltage is sent to the microcomputer. As the temperature of the PTC sensing element increases, its resistance increases and in turn the voltage signal to the microcomputer decreases. The microcomputer may then, for example, decrease the amount of power supplied to the heating elements, or may cut the power to the heating elements altogether.
In accordance with one aspect of the present invention, the PTC sensing element is formed by extruding a PTC compound onto a nonmetallic core or carrier. As an example, the nonmetallic carrier is a polymeric material, such as a polyester core.
Because the core of the PTC temperature sensing wire is nonmetallic, the sensing element is flexible and has a thin profile. In addition, the sensing element is lightweight, and thus does not add significant bulk to a warming blanket. Moreover, since the temperature sensing elements cover the warming blanket, it is possible to detect localized overheating in the warming blanket, no matter where the localized heating may occur in the blanket.
The fixed resistor requires very little additional PC board area and may be added to existing warming blanket controls with little effort or cost. As such, adding the resistor and microcomputer to conventional warming blanket controls requires very little modification.